Booster for explosive blasting agents

ABSTRACT

A booster for detonating cap-insensitive explosives is provided comprising a container having a main body portion and a neck portion of smaller cross-sectional area than the main body portion and having an opening in the neck portion for introduction of a detonating-fuse-insensitive explosive charge which fills the main body portion, and a detonating-fusesensitive explosive charge which fills the neck portion. The booster of the present invention is conveniently prepared and handled or loaded and has inherent water-resistance even though not necessarily water-proof and though inexpensive water-soluble explosive ingredients may be employed.

United States Patent [191 Cook [451 Apr. 29, 1975 I BOOSTER FOREXPLOSIVE BLASTING AGENTS [75] Inventor: Melvin A. Cook, Salt Lake City,

Utah

[73] Assignee: Ireco Chemicals, Salt Lake City,

Utah

[22] Filed: Apr. 6, 1973 21 Appl. No.: 348,767

OTHER PUBLICATIONS Military Explosives, TM 9-l9l0/TO ll A-l-34, Apr.1955, pp. 182, 183.

Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or Firm-Robert A.Bingham [57] ABSTRACT A booster for detonating cap-insensitiveexplosives is provided comprising a container having a main body portionand a neck portion of smaller cross-sectional area than the main bodyportion and having an opening in the neck portion for introduction of adetonatingfuse-insensitive explosive charge which fills the main bodyportion, and a detonating-fuse-sensitive explosive charge which fillsthe neck portion. The booster of the present invention is convenientlyprepared and handled or loaded and has inherent waterresistance eventhough not necessarily water-proof and though inexpensive water-solubleexplosive ingre clients may be employed.

14 Claims, 2 Drawing Figures BOOSTER FOR EXPLO'SIVE BLASTING AGENTS Thisinvention relates to an explosive booster for detonating cap-insensitiveexplosive compositions such as ammonium nitrate/fuel oil and aqueousblasting agents commonly referred to as slurry blasting agents orexplosives.

Many types of boosters have been used in the past for detonatingexplosive compositions. Conventional booster assemblies generallycomprise a cast or pressed high explosive charge having a well,indentation or hole capable of receiving a cap, or fuse-, type primaryinitiator. Many variations of this general assembly are found. Forinstance, the high explosive charge may be in a protective containerwith the hole or well extending into or through the charge and separatedfrom the body of high explosive by an extension of the container wall.Other booster assemblies comprise a compacted or cast core ofdetonating-fuse-sensitive explosive surrounded by a compacted or castsheath of highly brisant detonating-fuse-insensitive explosive andhaving one or more wells or bores extending through the core and sheathadaptable for receiving a detonating fuse or other primary initiator.When the detonating fuse is initiated, it in turn initiates thedetonating-cord-sensitive core which in turn initiates thedetonating-cordinsensitive sheath. Boosters of this latter type areshown in US. Pat. Nos. 3,037,452, 3,037,453, and 3,359,902. Theseboosters are generally not encased by a water-tight container andtherefore the cast or pressed explosive must be water-resistant, if theboosters are to be used in water-containing boreholes. ln application,boosters of this latter type can be placed singly or intermittently atappropriate spacings at or from the bottom to the top of a borehole.Such placement is accomplished by threading detonating fuse (whichgenerally runs the length of the borehole) through the bore of thebooster(s) and allowing the booster to slide down the fuse into theborehole at a proper sequence during the loading of the borehole withexplosive charge. Thus, the loaded an primed borehole may consist of aseries of appropriately spaced boosters threaded together by adetonating fuse downline (which may be tied at the down end to preventthe bottom booster from slipping off the line) all held firmly in placeby the explosive charge, which surrounds the boosters and fills theborehole. Generally, this boostering series would be located along theaxis of the explosive charge.

Threading boosters on a detonating fuse downline at approximateintervals during the filling of the borehole with an explosive charge isa convenient method of boostering. The booster of the present inventionis conveniently loaded and thereby also provides a convenient method ofboostering. The boosters of the present invention also have thebeneficial attributes of boosters having a protective container.

The booster of the present invention comprises a container of suitableshape and material having a main body portion and an elongated neckportion. The elongated neck portion has substantially lesscross-sectional area than the average cross-sectional area of the mainbody portion. The main body portion of the container is filled byconventional means to the base of the neck with adetonating-fuse-insensitive explosive charge which need not have anywater-resistant characteristic. The neck is then filled with adetonating-fuse-sensitive explosive which is essentiallywater-resistant. Detonating fuse may then be wrapped or tied around theperiphery of the neck so as to position the fuse in close proximity tothe detonating-fuse-sensitive explosive for initiation purposes. Theneck may have an outward extending lip at its opening to preventslippage of the detonating fuse off the neck.

Boosters of the present invention can be easily loaded and positioned ina borehole merely by wrapping or tying a detonating fuse downline aroundthe neck of the booster. Boosters can be attached in this manner atappropriate intervals along the length of the detonating fuse. Sincethese boosters are firmly attached along the detonating fuse downline,the series of boosters may be prepositioned in the borehole prior tofilling with the main explosive charge rather than positionedconcurrently during filling as is necessary when boosters having a boreare threaded on a fuse downline as described previously. The ability,when desired, to conveniently pre-position a series of boosters in theabove manner is one of the advantages of the present invention.

The exact mode of attaching the detonating fuse to the booster is notoverly critical and depends primarily on preference for manner ofhandling and loading the booster(s). For instance, a closed loop ofdetonating fuse having its ends embedded in the detonating-fusesensitiveexplosive charge could readily be used so long as close, positivecontact between fuse downline and loop was maintained. This would allowloading of the boosters in the conventional threaded manner, since thedetonating fuse downline could be threaded through the closed loop.Other attachment variations are possible.

A more detailed description of the present invention is obtained byreference to the accompanying drawings which depict representativeembodiments.

A detailed description of the drawings is as follows:

FIG. 1 is a cross-sectional front view of a booster of the presentinvention.

FIG. 2 is a cross-sectional front view of a booster container ofpreferred shape.

With reference to FIG. 1, a symmetrically circular container 1 is shownhaving an elongated neck 5 of smaller diameter than the average diameterof the main body of the container. Container 1 is flask-shaped to acertain degree due to the truncated cone-shaped portion connecting theneck 5. This general container shape is particularly advantageous forboosters of the present invention as will be explained below. At theopening 6 at the end of the neck of the container is a lip 3. Within thecontainer is an explosive charge 4 which is insensitive to detonation bya detonating fuse or detonating-fuse-insensitive and which fills themain body of the container to the base of the neck 5 as shown at 7.Filling the neck 5 of the container is a detonating-fuse-sensitiveexplosive charge 2. This fusesensitive charge functions somewhat as aplug for the container to provide water-resistance for thefuseinsensitive main body charge as will be explained below. Around thecircumference of the neck are two wrappings of detonating fuse 8. Thesewrappings are held in place around the neck by lip 3 that acts as abarrier to impede slippage of the fuse off the neck.

In application, the booster shown in FIG. 1 will be appropriatelypositioned so as to be in direct contact with an explosive charge in aborehole. The boostering system for the charge may be a single boosteror a series of spaced boosters all connected in series to the detonatingfuse. A single detonating fuse downline can be easily tied or wrappedaround the booster neck(s) and of the wave front and also produce asimilarly expanding wave front generally along the axis of the containerin the direction opposite the container opening, i.e., toward its base.In this manner the explosive energy of then the fuse and connectedbooster(s) can be lowered 5 the booster will be directed eesentiallyforward and into the borehole. Therefore, the booster or boostersoutward from its base thereby constituting a specifimay bepre-positioned in the borehole prior to filling cally directed and thusconcentrated boostering power with explosive charge. for the mainexplosive charge in the borehole. Al-

Once the boostering system described above is posithough the .boosterpower f f f l0 ward from its base, careful positioning or aligning oftioned and the borehole has been loaded with explosive f l I d f theaxis of the booster within the axis of the borehole charge and thesur-roun mg area y C ear-e 9r is not critical so long as the base of thebooster is enblasting, the detonating fuse is then initiated which willcom ed or s nded b ex losive char 6 It is in turn initiate thedetonating-fuse-sensitive high explogj j g g an X aspfar as j i d sivecharge in the neck of the booster container which p g p l5 practical,the axis of the booster with that of the borewill in turn initiate thedetonating-fuse-insensitive exhole so that the base of the booster facesthe main of plosive charge in the main body of the container. In thisthe ex losive char 6 Positionin the booster in this manner, completedetonation of the booster is accomp t g b t i plished. Detonation of thebooster or boosters will then mannef l l 00S ermg power 5 initiate theexplosive charge surrounding the boosters transmltte, to 6 exp Osweargej resulting in a successful explosion According to the presentinvention, boosters were prepared and tested and the results tabulatedas shown The booster Show F 1 has a flask or below in Table l. Theboosters tested comprised a a appearance whlch advantagaous for maxlmlz'homogenious mix main body explosive charge consistmg a i boosfer shock aexlaoswe as ing of 60 percent air dried TNT (trinitrotoluene), and asobtaining maximum efficiency in detonation of the 40 percent AN(ammonium nitrate) m ground to a mam f Upon aetonanon the detonatmg'particle size of 32 mesh or smaller. The ground AN fuse-sensitive highexplosive charge 2 in the neck 5 of prms used were Monsanto An explosivecharge container 1, caused by initiation of the circumferencmgcontaining a combination of AN and TNT is commonly dematmg fuse adetonatfon a from produced referred to in the art as amatol. Theconfiguration of during the detonatlon reacnon Wm expand laterally thecontainer used for the boosters tested is shown in outward andforwardfmm f charge generally 9 FIG. 2. The main body portion of thecontainer was apthe axis of the container. This shock wave expansionproximately 4 inches in length and 2 inches in width w ll generallyfollow the conical shape of booster conand the container neck portionwas approximately 1 1 tamer 1 which also extends i wa By inches inlength and 1 inches in diameter. The trunforming the shape of thecontainer containing the main 35 Gated cone portion of the main bodyportion connect booster charge (dctoatmg'fuse'msensftwe explos we ingthe neck portion was approximately nine-sixteenths charge) the Shape ofthe expanding detonauon inches in length. The containers used werebell-shaped wave front, all or most of the wave front energy W11l be inorder to maximize detonation efficiency and power transmitted throughall or most of the explosive charge as explained above. The highexplosive initiating to be initiated thereby maximizing boosterdetonation 40 Charge in the container neck comprised 40 to gramseffic'ency of a cast blend of /35 PETN (pentaerythritol tetrani- Themain booster charge initiated in this manner will trate)/TNT(trinitrotoluene) A combination of PETN undergo a detonation-reactionconforming to the shape and TNT is commonly referred to as pentolite.

TABLE I Testing Conditions Dctonating Fuse Rcsults*** Time in WaterPressure of Configuration Results*** Water Dry (0 days) 1 turn, 18 grainPC* 1, Failed do. 2 turns, l8 grain PC 1, Punched do. 1 turn, 25 grainPC 8. Punched do. 2 turns, 25 grain PC I, Punched 1 Day 50 psi 2 turns,25 grain PC I, Failed l, Punched l, Punched 3 Days 50 psi 2 turns, 25grain PC 1, Punched 2, Punched (50%) 4 Days 50 psi 2 turns, 25 grain PC2, Punched l, Dented (l%") l 1 Days 50 psi 2 turns, 25 grain 2, Failedthrough the plate. Percentage figure following Punchcd" indicates amountof total hole formed. i.c.. 7r

of hole circumference.

The boosters tested were prepared in the following manner: the ammoniumnitrate prills were uniformly mixed into and throughout molten TNT whichwas at a temperature of about 82 C and thereafter the fluid blend waspoured into the container filling the main body portion to the base ofthe neck. This charge (amatol) was then allowed to solidify. Thereafter,molten pentolite at a temperature of about 82 C was cast into the neckof the container and allowed to solidify. Casting was accomplished at oras close to the solidification temperature as possible so as toeliminate, as far as possible, air holes or pockets which may form dueto shrinkage of the charge upon cooling. Thus free space within thecontainer was minimized. Casting of most of the boosters was in factaccomplished after part of the TNT had crystalized but while the chargewas still easily pourable. Detonating fuse of type described in thetable was then tied around the periphery of the neck of the container inthe manner described in the table. Detonation results upon initiation ofthe detonating fuse were as shown.

As indicated in the table, some of the boosters were stored under waterpressure of 50 psi. for various periods of time. Although no specificattempt was made to make the containers watertight, the results showthat the boosters were still effective even after four days storageunder such circumstances. Thus, another important advantage of theboosters of the present invention is their inherent water-resistancyeven though they are not necessarily water-tight and even when awatersoluble explosive charge is used, e.g., AN is very soluble inwater.

Visual examination of the boosters after storage indicated that waterhad penetrated the inside of the container and in fact had surroundedthe amatol main body charge. The boosters were, however, stilleffective. Thus boosters of the present invention can be consideredwater-resistant even if not necessarily waterproof. This attributeallows their effective use in deep water-filled boreholes.

The inherent water-resistance of the boosters of the present inventionthat contain a water-soluble main explosive charge is attributed to thefact that dissolution of the soluble salt or ingredient contained withinthe main body explosive charge occurs only by the slow process ofdiffusion. The fuse-sensitive high explosive charge in the neck of thebooster (which itself must not be soluble or decomposable in water)functions to restrict the diffusion path area of dissolved salt oringredient to only that small area surrounding the periphery of thecharge between the container and the charge. Thus, boosters of thepresent invention can be stored under water for extended periods of timewithout any adverse water damage since only a very small amount ofsoluble explosive charge will have diffused out of the container.Extended water storage, however, may cause desensitization of the chargedue to water permeation throughout the entire body of the explosivecharge. As shown in the table, after 11 days water storage the boostersfailed to detonate. Casting or loading the boosters with explosivecharge should be accomplished so as to minimize air space or voidsbetween containerwall and charge and Within charge in order to minimizeamount of water intrusion. Different oxidizing salts such as any of thealkali or alkaline earth metal nitrates or chlorates and perchlorates aswell as different types or brands of the same salt can have asubstantial effect on the duration of effective water-resistancy. Forexample, potassium and ammonium perchlorates are much less soluble thanAN and would therefore provide better water-resistance.

Although AN is very soluble in water, it has a unique property whichprovides good water resistance. One important reason for the minimalamount of diffusion evidenced over extended water storage of boosterscontaining AN as part of the explosive charge is that AN swells involume upon dissolution thereby increasing the pressure within thecontainer, which would therefore tend to inhibit further dissolution andsubsequent diffusion. Any oxidizer salt or or water-soluble explosivecomponent having a similar property would be equally advantageous. Thus,even though watersoluble ingredients can be used in boosters of thepresent invention since only a limited degree of diffusion occurs asexplained above, it is preferable to use those soluble ingredients suchas AN which swell in volume upon dissolution.

Another major advantage of the present invention is that relativeinexpensive inorganic oxidizing salts or other inexpensive ingredientscan be combined in relatively high proportion with a more expensive highexplosive ingredient such as TNT to form the fuseinsensitive, main bodycharge of the explosive. This combination results in a significantlyless expensive booster than those comprised of high explosiveingredients such as TNT, RDX, PETN, and the like and mixtures of these.Less expensive ingredients such as AN function not only as a bulk fillerof the booster container volume thereby reducing the amount of moreexpensive explosive required, but also as participating explosiveingredients which enter into the detonation reaction and provide for amore oxygen-balanced charge. The use of inorganic oxidizer salts incombination with high explosive will generally result in a lowercost/energy value than when high self-explosive is singularly used. Forexample, amatol having a composition of 60% TNT and 40% AN hascost/energy value of about 34 cents/million calories, whereas TNT has asimilar value of about 51 cents/million calories. The preferred range ofinorganic oxidizing salt would be 20 to 60 percent by weight, andcorrespondingly high explosive to 40 percent. The use of theseinexpensive, and usually soluble ingredients is made possible by theinherent water-resistancy of the boosters as explained above.

The fuse-sensitive high explosive charge for the neck of the boostermust not be soluble or decomposable in water in order to function as :aplug to prevent water degradation of the booster as explained above. Apreferred fuse-sensitive charge is pentolite having a range of PETN of50 to 65 percent by weight, depending upon desired sensitivity andpourability or castability, and a corresponding 50 to 35 percent byweight range of TNT.

The size and shape of the container can be varied to any desired degree.Although the high explosive charge contained within the neck of thecontainer is adequate to prevent substantial water impairment overrelatively extended storage periods, a cap or similar device may beplaced over the neck opening to essentially prevent or impede waterintrusion and impairment. The material of the container is not criticalbut should be durable in the environment present in the borehole andcompatible with the explosive contents. Polyethylene is a preferredcontainer since it can be easily blow molded into any desired containershape and is relatively inexpensive.

The invention described above offers outstanding advantages in providinga booster which is inexpensive, conveniently manufactured and applied inthe field and water-resistant. Although the present invention wasdescribed in terms of using detonating fuse as the primary initiator, itis obvious to one skilled in the art that a cap primary initiator couldbe used to detonate the boosters with appropriate attachment to orplacement in the detonating-fuse-, or cap-, sensitive explosive charge.

It will be obvious that modifications mentioned above and others notmentioned may be made by those skilled in the art without departing fromthe spirit and purpose of the invention. It is intended to cover theinvention and obvious variations and modifications as broadly as theprior art permits.

What is claimed is:

1. A water-resistant booster for detonating capinsensitive explosiveblasting agents comprising a. a container having a main body portion andan elongated neck portion of smaller-cross-sectional area than the mainbody portion and having an opening at the end of the neck portionopposite main body portion,

b. an at least partially water-soluble detonating fuseinsensitiveexplosive charge within the main body portion of said container, and

c. a water-insoluble detonating fuse-sensitive explosive chargesubstantially wholly contained within the neck portion of said containerand having an outer peripheral surface which conforms to the innersurface of the neck portion throughout at least most of the chargesouter peripheral surface to provide close contact therewith and therebyto allow said charge to plug said container.

2. A booster according to claim 1 wherein said detonatingfuse-insensitive explosive is a combination of a high explosive and aninorganic oxidizing salt selected from the group which consists ofalkali or alkaline earth metal nitrates, chlorates and perchlorates.

3. A booster according to claim 2 wherein said inorganic oxidizing saltis ammonium nitrate.

4. A booster according to claim 2 wherein said high explosive istrinitrotolune.

5. A booster according to claim 3 wherein said high explosive istrinitrotoluene.

6. A booster according to claim 5 wherein ammonium nitrate is present inamount of about 40 percent by weight and trinitrotoluene is present inamount of about 60 percent by weight.

7. A booster according to claim 1 wherein said detonating fuse-sensitiveexplosive is a combination of trinitrotoluene and pentaerythritoltetranitrate.

8. A booster according to claim 1 wherein said container is flask orbell-shaped to conform to a forward, laterally outward, expandingdetonation wave front obtained upon detonation of said detonatingfusesensitive explosive within the neck portion and which wave frontproceeds axially through the main body portion.

9. A booster according the claim 1 wherein material of said container ispolyethylene.

10. A booster according to claim 1 wherein saiddetonating-fuse-insensitive explosive contains a soluble ingredientwhich swells in volume upon dissolution in an aqueous medium.

11. A method of preparation of the booster of claim 1 comprising theconsecutive steps of v a. filling the main body portion of saidcontainer with said detonating-fuse-insensitive explosive,

b. filling the neck portion of said container with saiddetonating-fusesensitive explosive, and

c. securing a detonating fuse in close proximity to saiddetonating-fuse-sensitive explosive.

12. A method according to claim 11 wherein said filling of saidcontainer with said detonating-fuse-, sensitive and insensitiveexplosive charges is accomplished by casting said explosive charges intosaid container in molten form at or close to solidification temperatureof said explosive to minimize voids or free space which may result uponsolidification of said explosive charges.

13. A method of boostering a borehole filled with cap-insensitiveexplosive charge using the booster of claim 1 comprising axiallypositioning said booster or series of said boosters into a borehole bysecuring said booster(s) to a detonating fuse downline at desiredposition or intervals along the length of the detonating fuse.

14. A method according to claim 13 wherein said booster or series ofsaid boosters is pre-positioned in the borehole before the borehole isfilled with the explosive charge.

1. A water-resistant booster for detonating cap-insensitive explosiveblasting agents comprising a. a container having a main body portion andan elongated neck portion of smaller-cross-sectional area than the mainbody portion and having an opening at the end of the neck portionopposite main body portion, b. an at least partially water-solubledetonating fuseinsensitive explosive charge within the main body portionof said container, and c. a water-insoluble detonating fuse-sensitiveexplosive charge substantially wholly contained within the neck portionof said container and having an outer peripheral surface which conformsto the inner surface of the neck portion throughout at least most of thecharge''s outer peripheral surface to provide close contact therewithand thereby to allow said charge to plug said container.
 2. A boosteraccording to claim 1 wherein said detonating fuse-insensitive explosiveis a combination of a high explosive and an inorganic oxidizing saltselected from the group which consists of alkali or alkaline earth metalnitrates, chlorates and perchlorates.
 3. A booster according to claim 2wherein said inorganic oxidizing salt is ammonium nitrate.
 4. A boosteraccording to claim 2 wherein said high explosive is trinitrotolune.
 5. Abooster according to claim 3 wherein said high explosive istrinitrotoluene.
 6. A booster according to claim 5 wherein ammoniumnitrate is present in amount of about 40 percent by weight andtrinitrotoluene is present in amount of about 60 percent by weight.
 7. Abooster according to claim 1 wherein said detonating fuse-sensitiveexplosive is a combination of trinitrotoluene and pentaerythritoltetranitrate.
 8. A booster accorDing to claim 1 wherein said containeris flask or bell-shaped to conform to a forward, laterally outward,expanding detonation wave front obtained upon detonation of saiddetonating fuse-sensitive explosive within the neck portion and whichwave front proceeds axially through the main body portion.
 9. A boosteraccording the claim 1 wherein material of said container ispolyethylene.
 10. A booster according to claim 1 wherein saiddetonating-fuse-insensitive explosive contains a soluble ingredientwhich swells in volume upon dissolution in an aqueous medium.
 11. Amethod of preparation of the booster of claim 1 comprising theconsecutive steps of a. filling the main body portion of said containerwith said detonating-fuse-insensitive explosive, b. filling the neckportion of said container with said detonating-fuse-sensitive explosive,and c. securing a detonating fuse in close proximity to saiddetonating-fuse-sensitive explosive.
 12. A method according to claim 11wherein said filling of said container with said detonating-fuse-,sensitive and insensitive explosive charges is accomplished by castingsaid explosive charges into said container in molten form at or close tosolidification temperature of said explosive to minimize voids or freespace which may result upon solidification of said explosive charges.13. A method of boostering a borehole filled with cap-insensitiveexplosive charge using the booster of claim 1 comprising axiallypositioning said booster or series of said boosters into a borehole bysecuring said booster(s) to a detonating fuse downline at desiredposition or intervals along the length of the detonating fuse.
 14. Amethod according to claim 13 wherein said booster or series of saidboosters is pre-positioned in the borehole before the borehole is filledwith the explosive charge.